If I made a good armature, can I use it for another mesh as well?
You can absolutely reuse armatures among meshes, and doing so allows you to bring over NLA actions and other animations associated with the armature. It's not trivial to do this, since both meshes must be weight painted to the needs of the armature and bones... but since you will probably accumulate a lot of animations over time, it is a good investment for important characters, or those that have a lot of actions.

I use common armatures for sea turtles, fish, mosasaurs, dinosaurs of a common body plan, etc, and the whole mixamo concept is based on the idea that yo will accumulate and use common armatures.



Additional information: how to copy a rig to another mesh

Mixamo: https://www.mixamo.com/#/ -- Thgis is not Blender specific, but a handy way to see how others have animated particular sequences and their files will work with Blender. You would be downloading an FBX, and importing into Blender via File | Import FBX.